Author

Award Date

Degree Type

Degree Name

Department

Geoscience

First Committee Member

Stephen Rowland

Second Committee Member

Joshua Bonde

Third Committee Member

Ganqing Jiang

Fourth Committee Member

Allen Gibbs

Number of Pages

85

Abstract

The early Cambrian was a period of transition during which the seafloor environment was changing from a microbial-mat-dominated environment to a bioturbation-dominated environment. The result was a patchy landscape of variable food resources for foraging burrowers to exploit. Looping trace fossils, such Psammichnites gigas and Taphrhelminthopsis nelsoni, appear in strata worldwide during this transitional period, and the ecological niche they filled is a subject of debate among ichnologists. The objectives of this study are (1) to determine the foraging strategies preserved by looping traces through the application of optimal foraging theory and quantitative analysis, and (2) use those results to determine the relationships between paleoenvironmental conditions, neurological complexity, and foraging behavior. These data are used to test three hypotheses for the purpose of looping behavior preserved in Cambrian trace fossils: (1) looping is inefficient active feeding behavior, (2) looping is search behavior, and (3) looping is an optimal foraging strategy in environments with densely packed and high quality patches.

In order to explore how the distribution and quality of food patches influence foraging behavior, I apply optimality models, such as marginal value theorem, from contemporary animal behavior theory to looping and meandering trace fossils. I use fractal dimension analysis and goniograms as quantitative analysis methods for quantifying trace fossils, in order to compare the foraging strategies preserved in looping and meandering traces, and also to test the possible relationship between trace fossil patterns and environmental conditions.

Results suggest that the P. gigas tracemaker utilized looping as search behavior. I conclude that the tracemaker used chemoklinotaxis or chemotropotaxis to find an external attractant from a food patch, while the T. nelsoni tracemaker used looping as an optimal foraging strategy. Cambrian tracemakers used looping as an optimal foraging strategy in an environment with densely packed, high-quality food patches, while those that used a meandering foraging pathway did so in widely dispersed, low-quality food patches. Fractal dimension analysis and the succession of shorter to longer foraging pathways may be used as a proxy for patch quality and density in a given environment. Environmental quality, rather than neurological complexity, is the primary driver for complex trace morphology.